1. Field of the Invention
The present invention relates to a vibratory plating method which improves plating efficiency by vibrating a plating container with plating liquid therein to maintain a uniform concentration of metal ions in the vicinity of cathodes.
2. Description of the Prior Art
In a conventional plating method using a barrel, workpieces are inserted in a plating liquid in the barrel and the barrel is rotated or rocked to bring the workpieces into sliding contact with cathodes and subject the workpieces to electrodeposition. Barrel type plating methods include one using an open-top bottle type barrel which is rotated while being inclined, and another one using a rectangular or cylindrical barrel having small apertures in the entire wall thereof and being horizontally disposed in a plating liquid, and rotated or rocked to agitate the plating liquid to effect the plating of the workpieces. In the use of an inclined barrel type plating apparatus, the temperature and the concentration of the plating baths are frequently subject to changes, the insertion and withdrawal of workpieces cannot be easily carried out, and anodes having a large surface area cannot be employed.
In the horizontal barrel type plating method using a horizontal barrel type plating apparatus, an electric current flows through small apertures in the side wall of the barrel. Thus the plating container requires a far higher voltage than the plating container used in other plating methods in which workpieces are suspended in a plating liquid. As a result, a large amount of energy is consumed, and sparks jump across the contacts of cathode lead wires and workpieces so that the surfaces of workpieces are burnt or have holes made therein by burning. In addition, the power source and other parts will often be damaged and the plating operation cannot be conducted smoothly in many cases.
Plating with 3-4 microns of nickel cannot be carried out efficiently in a horizontal barrel type plating apparatus or it usually requires 60 to 90 minutes of electrodeposition even if the diameters of the apertures in the side wall of the plating barrel are increased. In addition, the amount of plating liquid removed from the plating barrel in a method using this apparatus is larger than that in a widely used plating method carried out with workpieces suspended in a plating liquid. This causes the composition of the plating bath to be changed. In other words, quality control cannot be carried out easily. The large amount of plating liquid removed from the plating barrel has caused trouble in the treatment of the waste water which is necessary for preventing the occurrence of environmental pollution, and has adversely affected the economy of the plating process.
These conventional plating processes have many other drawbacks in addition to those described above. They have a low productivity and the apparatus used requires a large floor space. Consequently, the quantity and dimensions of the workpieces to be plated are limited. In fact, the conventional barrel type plating processes have many problems yet to be solved including the above-mentioned problem of treatment of the waste water. Namely, in a conventional barrel type plating method, the plating of workpieces cannot be satisfactorily carried out unless they are soaked completely in a large amount of plating liquid while being rotated or rocked. Moreover, the coating plated on the workpieces does not have a uniform thickness on each part of the surfaces because of sufficient agitation of the plating liquid.